One of the most powerful and far-reaching theoretical models ever devised, already introduced in these pages, is Einstein’s general theory of relativity—but you can call it GR after you get to know it better. Published in 1916, GR outlines the relevant mathematical details of how everything in the universe moves under the influence of gravity. Every few years, lab scientists devise ever more precise experiments to test the theory, only to further extend the envelope of the theory’s accuracy.
